Hibernate 单项多对1

自己理解：

单向1对多。
一个客户可以发出多个订单。但是一个订单只属于一个客户。
写对象的时候。在多的那个类对象把1的作为自己的一个属性。
写配置文件
<many-to-one  name=1的属性名。class=1的类名。column=1的主键名>

多的1方的Java类。 把1的作为一个属性放到多的里面。

package com.hibernate.n21;

public class Order {
    private Integer orderId;
    private String orderName;
    private Customer customer;
    private Integer getOrderId() {
        return orderId;
    }
    public void setOrderId(Integer orderId) {
        this.orderId = orderId;
    }
    public String getOrderName() {
        return orderName;
    }
    public void setOrderName(String orderName) {
        this.orderName = orderName;
    }
    public Customer getCustomer() {
        return customer;
    }
    public void setCustomer(Customer customer) {
        this.customer = customer;
    }
    public Order(String orderName, Customer customer) {
        super();
        this.orderName = orderName;
        this.customer = customer;
    }
    
}

映射文件：

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.hibernate.n21">

    <class name="Order" table="orders" >
        
        <id name="orderId" type="java.lang.Integer">
            <column name="order_Id" />
            <!-- 指定主键的生成方式, native: 使用数据库本地方式 -->
            <generator class="native" />
        </id>
    
        <property name="orderName"
            type="java.lang.String" column="order_Name" >
        </property>
        
        <!-- 映射n-1的关联关系  
　　　　　　　　name:1的属性名。把1当成多的一个属性。
　　　　　　　　class  1的类名。
　　　　　　　　column   1的主键名。
 -->
        <many-to-one name="customer" class="Customer" column="customer_Id"></many-to-one>        
    </class>
    
</hibernate-mapping>

1的类名：

package com.hibernate.n21;

public class Customer {
    private Integer customerId;
    private String customerName;
    
    public Integer getCustomerId() {
        return customerId;
    }

    public void setCustomerId(Integer customerId) {
        this.customerId = customerId;
    }

    public String getCustomerName() {
        return customerName;
    }

    public void setCustomerName(String customerName) {
        this.customerName = customerName;
    }

    public Customer() {
        super();
    }

    public Customer(String customerName) {
        super();
        this.customerName = customerName;
    }
    
    
}

映射文件：

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.hibernate.n21">

    <class name="Customer" table="customer" >
        
        <id name="customerId" type="java.lang.Integer">
            <column name="customer_Id" />
            <!-- 指定主键的生成方式, native: 使用数据库本地方式 -->
            <generator class="native" />
        </id>
    
        <property name="customerName" 
            type="java.lang.String" column="customer_Name" >
        </property>
        
    </class>
    
</hibernate-mapping>

然后在主的映射文件hibernate.cfg.xml文件中加上映射

　　　　　<mapping resource="com/hibernate/n21/Customer.hbm.xml"/>
        <mapping resource="com/hibernate/n21/Order.hbm.xml"/>

 SAVE():

 1 先保存1的一端  只是三条insert语句。
 2 @org.junit.Test
 3     public void testN21Save(){
 4         Customer customer=new Customer();
 5         customer.setCustomerName("C1");
 6         Order order1 =new Order();
 7         order1.setOrderName("O1");
 8         Order order2 =new Order();
 9         order2.setOrderName("O2");
10         
11         //设置关联关系。就是给多的一方设置外键
12         order1.setCustomer(customer);
13         order2.setCustomer(customer);
14         session.save(customer);
15         session.save(order1);
16         session.save(order2);
17         
18     }
 1 先保存多的一端。3条insert语句。2条update语句
     因为在插入多的一端时，无法确定1的一端的外键值。所以只能先为null。等1的一端插入后。再进行修改。
 2 @org.junit.Test
 3     public void testN21Save(){
 4         Customer customer=new Customer();
 5         customer.setCustomerName("C1");
 6         Order order1 =new Order();
 7         order1.setOrderName("O1");
 8         Order order2 =new Order();
 9         order2.setOrderName("O2");
10         
11         //设置关联关系。就是给多的一方设置外键
12         order1.setCustomer(customer);
13         order2.setCustomer(customer);
14         
15         session.save(order1);
16         session.save(order2);
17         session.save(customer);
18     }

 select()方法：

如果在第5行关闭session。就会出现懒加载异常。因为System.out.println(order.getCustomer().getClass());  class com.hibernate.n21.Customer_$$_javassist_0
得到的是一个customer代理对象。
1 @org.junit.Test
2     public void testN21Select(){
3         Order order=(Order) session.get(Order.class, 5);
4         System.out.println(order.getOrderName());
5         session.close();
6         Customer customer = order.getCustomer();
7         System.out.println(customer.getCustomerName());
8     }

对于懒加载异常。我们可以在hibernate.cfg.xml中设置立即加载。

<class name="Customer" table="customer" lazy="false">    我们设置懒加载为否。就是立即加载

Update():

@org.junit.Test
    public void testN21Update(){
        Order order=(Order) session.get(Order.class, 5);
        Customer customer=order.getCustomer();
        customer.setCustomerName("N21Update");
    }

Delete:

//删除多的，直接删除
@org.junit.Test
    public void testN21Delete(){
        Order order=(Order) session.get(Order.class, 5);
        session.delete(order);
    }
//不设置级联删除的话。删除1的一方。会出现异常。因为1的一方。对应好几个  
//但是1的一方没有被引用的话。是可以删除的

1 @org.junit.Test
2     public void testN21Delete(){
3         Customer customer=(Customer) session.get(Customer.class, 3);
4         session.delete(customer);
5     }
org.hibernate.exception.ConstraintViolationException: could not execute statement
    at org.hibernate.exception.internal.SQLExceptionTypeDelegate.convert(SQLExceptionTypeDelegate.java:74)
    at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:49)
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:125)
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:110)
    at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:136)
    at org.hibernate.engine.jdbc.batch.internal.NonBatchingBatch.addToBatch(NonBatchingBatch.java:58)
    at org.hibernate.persister.entity.AbstractEntityPersister.delete(AbstractEntityPersister.java:3343)
    at org.hibernate.persister.entity.AbstractEntityPersister.delete(AbstractEntityPersister.java:3546)
    at org.hibernate.action.internal.EntityDeleteAction.execute(EntityDeleteAction.java:100)
    at org.hibernate.engine.spi.ActionQueue.execute(ActionQueue.java:377)
    at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:369)
    at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:293)
    at org.hibernate.event.internal.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:339)
    at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:52)
    at org.hibernate.internal.SessionImpl.flush(SessionImpl.java:1234)
    at org.hibernate.internal.SessionImpl.managedFlush(SessionImpl.java:404)
    at org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.beforeTransactionCommit(JdbcTransaction.java:101)
    at org.hibernate.engine.transaction.spi.AbstractTransactionImpl.commit(AbstractTransactionImpl.java:175)
    at com.hibernate.n21.Test.destroy(Test.java:39)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:37)
    at org.junit.runners.BlockJUnit4ClassRunner.runNotIgnored(BlockJUnit4ClassRunner.java:79)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:71)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:49)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:236)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot delete or update a parent row: a foreign key constraint fails (`luwei`.`orders`, CONSTRAINT `FK_qaw4j85b8ppgne3sg6f218msv` FOREIGN KEY (`customer_Id`) REFERENCES `customer` (`customer_Id`))
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
    at com.mysql.jdbc.Util.getInstance(Util.java:381)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1015)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:956)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3515)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3447)
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1951)
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2101)
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2554)
    at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1761)
    at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2046)
    at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1964)
    at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1949)
    at com.mchange.v2.c3p0.impl.NewProxyPreparedStatement.executeUpdate(NewProxyPreparedStatement.java:147)
    at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:133)
    ... 37 more
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原文地址：https://www.cnblogs.com/bulrush/p/7789010.html